1. Field of the Invention
The present invention relates to a variable valve lift apparatus of an engine, and more particularly to a variable valve lift apparatus of an engine, capable of controlling the degree of lift of a valve according to driving conditions of a vehicle.
2. Description of the Related Art
A valve mechanism applied to a vehicle engine supplies fuel-air mixture to a combustion chamber and discharges combustion gas.
Recently, variable valve mechanisms have been developed to optimize an inflow of the fuel-air mixture and a discharge efficiency of the combustion gas by varying an opening rate or an opening phase of a valve depending on operating areas of an engine which are divided according to operating conditions of the engine, that is, the rotation speed and the load of the engine, and applied to the engine.
Accordingly, the variable valve mechanisms for a vehicle engine can enhance the performance of the engine, such as the fuel efficiency, the torque, or the power of the engine, and reduce an amount of discharged gas.
The variable valve mechanism for the vehicle engine includes a variable valve timing mechanism to vary the opening phase of the valve, a variable valve lift mechanism to vary the opening rate of the valve, and a variable valve operating angle mechanism to vary the operating angle of the valve.
Among them, the variable valve lift mechanism is used to enhance the power and the fuel efficiency of the vehicle at middle and low-speed modes, and classified into rock arm, pivot, tappet, and bucket-type variable valve lift mechanisms.
Applicant of the present invention has multiple disclosures including patent documents (Korean Patent Registration Nos. 10-1084739 and 10-1084741 (issued on Nov. 22, 2011) and Korean Unexamined Patent Publication No. 10-2012-0088363 (filed on Aug. 8, 2012) related to the variable valve lift mechanism.
However, according to the variable valve lift mechanism of the related art, the displacement of an intake valve is always constant regardless of the load of the vehicle, so that an engine speed to represent the optimal efficiency may be restricted.
Accordingly, there is required a technology of deactivating a portion of cylinders at a low-speed and low-load state and activating an entire portion of the cylinders at a high-speed and high-load state to improve the efficiency of the engine.
Meanwhile, conventionally, although hydraulic pressure is used to deactivate a valve or control the valve in two stages, the structure of the variable valve lift mechanism becomes complicated, so that the workability may be degraded.
In addition, when the hydraulic pressure is used, the viscosity of hydraulic oil reacts sensitively to the temperature, so that the hydraulic pressure may be changed. Accordingly, the variable valve lift mechanism erroneously operates so that the precision may be degraded when adjusting the degree of the lift of the valve.